The present invention relates to a battery pack and a method of producing the same, and more particularly to a battery pack in which a polymer battery comprising a sheath material consisting of a laminated film is contained in an outer case, and a method of producing the same.
In recent years, portable electronic apparatuses such as camera-integrated type VTR (videotape recorder), cellular phones, notebook type personal computers, etc. have appeared, and reductions in the size and weight thereof have been contrived. Attendant on this, as to a driving power source for such a portable electronic apparatus, an increase in capacity and a further reduction in size have come to be keenly demanded. As this type of driving power source, the so-called polymer battery comprising a polymer cell contained inside a laminated film has been put to practical use. It is being investigated to contain such a polymer battery further into an outer case, in view of the need to protect the polymer battery from external shocks, scratching or the like.
Hitherto, as an outer case for containing the cell main body therein, an outer case with the split-in-two structure consisting of a combination of an upper-lower pair of case halves formed of a synthetic resin which are produced by molding (hereinafter referred to simply as the resin-made outer case) has been in general use. More specifically, it has been practiced to dispose the cell main body in one of the case halves, put the other of the case halves thereon, and join the peripheral contact surfaces of the case halves to each other by ultrasonic welding or the like, thereby obtaining a battery pack.
In the above-mentioned resin-made outer case, a material thickness of about 0.3 to 0.4 mm is needed, for protecting the cell main body disposed therein from external shocks and the like. In addition, in the resin-made outer case, it is necessary to fix the cell element to one of the case halves by an adhesive or a double-coated tape, for preventing the cell main body from chattering inside the case, for reinforcement in case of falling, or for other purposes. Furthermore, taking into account the tolerance at the time of molding the case halves, in the case of the resin-made outer case, the overall thickness of the battery pack is determined by adding the thickness of portions not contributing to the cell capacity of about 1 mm to the thickness of the cell main body which is the power generation element.
Besides, in the resin-made outer case, in the case of joining the upper-lower pair of case halves to each other by ultrasonic welding, a material thickness of 0.7 to 1 mm is required at the joint portions in order to obtain sufficient strength for enduring the welding.
Thus, in the case of using the resin-made outer case, the portion which is necessary on a structural basis but which does not contribute to cell capacity is bulky, so that it has been difficult to achieve a further reduction in size and a further increase in capacity.